Generally, a shaft locking device is used in power tools like drills and screwdrivers. A shaft locking device allows a user to manually tighten the screws by turning a housing of the power tool after the screws are initially secured using a motor shaft. Further, when the battery is fully discharged, the shaft locking device allows the power tool to still be used to tighten or loosen screws manually by turning the housing of the power tool. In other words, the shaft locking device prevents the output shaft from turning separate from the screwdriver housing.
Other screwdrivers also have an additional circumferential direction impact function. For example, the output shaft driven by the motor may provide an additional circumferential contact position while tightening a screw which increases the effectiveness of the screwdriver.